The objectives of the present project are to study the potential role of various environmental components, such as lighting schedule, thermal conditions, nutrition and population density, in the process of sexual maturation. Current efforts are devoted to a study of the normal sequence of endocrine events which lead to puberty in male and female rats under control conditions. All endocrine variables are measured in the same individuals. Pituitary and serum gonadotropins and prolactin are measured by radioimmunoassay. Hypothalamic releasing factor activity will be estimated by in vitro incubation techniques. Gonadal steroid levels in systemic blood and secretion rates into ovarian or testicular vein will be measured by radioimmunoassay or gas-liquid chromatography following purification. These experiments will be used to evaluate the initial change in sensitivity (positive or negative) along the hypothalamic-pituitary-gonadal axis, which leads to an expression of full functional capacity in the entire reproductive system. These studies will be followed by experiments which will investigate the role of the above mentioned environmental components on the process of sexual maturation. Environmental components will be altered individually. All other variables will be held constant. Animals will again be examined for the same critical endocrine events which were monitored in the previous control studies. Particular attention will be paid to initial critical events which may have been elucidated in previous sequential analyses. If any defined changes in the normal endocrine sequences can be established, we will attempt to mimic such alterations by ablation, antibody blocking technique or exogenous hormone administration.